Ventilation for factories that yields acceptable indoor climate conditions is often difficult to achieve. Various methods are practiced in the art but do not work in a cost effective and energy efficient method. Some of the various methods practiced include non-interconnected use of fuel-fired air make-up heaters, exhaust fans, "microventilation" spot cooling, door air curtains, and speed-door closures.
In industrial factories, particularly in the powder metal industry, which have a "clean" but high level of internal heat gain generated from the industrial process, excess heat causes several problems such as difficulty in maintaining positive air pressure within the factory (i.e., the atmospheric pressure within the factory is equal to or greater than the atmospheric pressure outside the factory). Generally speaking, factories need to take in air from the outside to cool the factory and facilitate combustion processes. The amount of intake air that a factory needs depends on the factory's operations and ventilation requirements. These aforementioned problems are exacerbated if the industrial factory has only a modest need for outside air intake to supply the factory's combustion and draft air because the modest intake is not sufficient to cool all of the generated excess heat. Air conditioning to counteract the excess heat is not a viable economic option because it is expensive to install, operate, and maintain.
The problems are most noticeable at the changing of the seasons. In addition to the obvious problem of keeping the factory at a comfortable temperature for the factory workers, excess heat generated from an industrial process causes other significant problems. During the warmer months when doors and windows are usually left open, the excess heat can easily be drawn away from the factory through the use of exhaust fans and gravity ventilators. However, during the cooler months when doors and windows are kept closed, use of exhaust fans or gravity ventilators causes negative pressure within the factory. Negative pressure causes particulates or combustion gases that may be contained in gravity flues are trapped within the factory. This is particularly dangerous when there is a large amount of carbon monoxide present in the factory process. The negative pressure within the factory keeps the carbon monoxide within the walls of the factory, poisoning the persons inside the plant.
In addition to trapping combustion gases and particulates within the factory walls, the negative pressure in the factory causes large intakes of outside air whenever a door or window is opened. This causes large volumes of cold air to flow into the factory at the floor level that, in turn, causes a loss of temperature control in the outlying areas of the factory. Some factories use fuel-fired air heaters to make up for the building-pressure control air and to provide heat to workers in the outlying areas of the factory. These fuel-fired air heaters are expensive pieces of equipment and operate inefficiently for making up for the building's negative pressure.